I was under the impression if you got to the crewroom before being notified of the delay you were technically on duty and thus you were limited by your time off requirements - I remember one crewmember who would instruct crewing on what he was and was not going to do - luckily he had a permanant contract!
If it was my airline he wouldn't be legal, as he's been on duty for 16hrs 5minutes - thus he needs 17hrs 5mins off. Meaning he can come back on duty for 13.05z.
Of course, he could always ring in fatigued, and if he was pulled up on it, it wouldn't do any harm to throw in crewing's 'suggestions'.
Horgy